The basic teaching for the manufacture of an elastic leg band diaper is found in U.S. Pat. No. 4,081,301 and consists of stretching the elastic ribbons, maintaining tension therein, and intermittently applying adhesive to selected portions of the elastic corresponding to the contractable leg portion of the diaper. Intermittent operation of devices used for applying adhesives is commonly accepted--but requires adhesives within a fairly narrow range of viscosity since the adhesive must be responsive to on-off operation of the nozzles or other applying means. Because the adhesive in such a situation must be fluid enough to be responsive, it lacks the higher tack characteristic of more desirable adhesives having higher viscosity. These more desirable adhesives, if used in on-off situations, cause plug-up and stringing problems, require sensitive heat control and expensive applying devices.
However, limiting the length of ribbon adhered to the underlying web results in that only selected portions of the diaper are shirred or gathered when the ribbon tension is relaxed. Further, the non-glued portions of the ribbon due to being unattached, do not cause gathering and also, upon relaxation of tension, retreat to normal length and are hidden inside the diaper.
On the other hand, with adhesives having higher viscosities and therefore higher tack, which could be used if the adhesive stripe were put down continuously, the deleterious effects of creep or slippage on the long term storage exposure to higher temperatures are avoided. However, the prior art expedients relative to continuous glue application involve either much higher cost materials or the addition of a release medium which must also be placed on the substrate intermittently.
For example, U.S. Pat. No. 4,300,967 teaches the use of a thermoplastic elastomeric material for the continuous ribbon and requires special equipment including heated rolls, chill rolls, etc., to immobilize or render inert spaced portions of the adhesive equipped elastic ribbon which correspond to the ends of the diaper.
U.S. Pat. No. 4,353,762 teaches the use of a release medium applied to intermittent spaced portions of the moisture impervious web while the adhesive is applied continuously to the stretched ribbon. Thereafter, the ribbon adheres almost instantaneously to the impervious web but will not adhere to those portions covered with the release medium. However, this again requires complicated equipment and the expenditure of additional money for materials not needed. In both cases, there is a "canceling out" of the activity of the adhesive.